It is well known that internal combustion engines generate exhaust streams whose components are not fully combusted, resulting in discharge of high pollutant levels. Two-cycle internal combustion engines, such as those used in motorcycles or various watercraft, tend to be the heaviest polluters. Personal watercraft, such as JETSKI, are known to discharge approximately thirty percent of their fuel to the body of water in which they are being used. These discharges foul the water and can result in downstream pollution of potable water supplies. Additionally, discharge of these uncombusted fuels into potable or recreational water supplies can create additional hazards due to the inclusion of other hazardous chemicals, such as methyl tetra-butyl ether (MTBE), in these fuels. MTBE is an additive used in California to reduce air pollutant levels from internal combustion engines. Although MTBE appears to provide cleaner combustion to minimize atmospheric or air pollution, uncombusted fuel containing MTBE can easily contaminate a water source. Unfortunately, MTBE is a suspected carcinogen. Discharge of uncombusted hydrocarbons and their associated chemical components to the atmosphere and waterways is a nationally recognized problem.
The prior art teaches several devices for completing the combustion of uncombusted hydrocarbon fuel expelled in the exhaust stream of a combustion engine. Some of these "combustors" require the addition of other fuel to supplement and maintain the burn required to fully oxidize the uncombusted exhaust components. This method increases fuel consumption and can result in higher levels of pollutant discharge.
Other types of combustors operate on a batch, rather than continuous, process. A batch process is most suitable where an engine may be shut down for a sufficient period of time to allow the uncombusted hydrocarbons to be burned off. This method is not suitable to applications, such as watercraft with two-cycle engines, where the volume of uncombusted fuel is substantial and not readily stored for subsequent burnoff.
Most notable of the prior art with reference to the present invention is a combustor invented by Naegeli (U.S. Pat. No. 5,584,178). The primary components of the Naegeli combustor include a combustion chamber and flame holder, with ignition means provided by a standard single sparkplug. Naegeli's combustor is shown installed in the exhaust piping from the internal combustion engine of a vehicle.
The Naegeli combustor is dependent on the ability of its flame holder to maintain a flame front to hopefully contact and burn off the uncombusted fuel components entrained within the exhaust stream of the internal combustion engine. It appears that the primary intended use for Naegeli's combustor is to preheat engine exhaust sufficiently to avoid fouling downstream exhaust treatment devices, such as a catalytic converter. Further, Naegeli's combustor uses a single sparkplug primarily to initiate combustion and establish a flame front on the flame holder; the "held flame" then theoretically provides the ignitive energy to continuously oxidize entrained combustibles in the exhaust stream. Naegeli describes an alternative embodiment of his invention which includes four sparkplugs uniformly dispersed about the circumference of one end of the combustion chamber. Even with four spark plugs, Naegeli's combustor provides insufficient ignitive energy via electrical arcing to provide reliable, continuous operation to ensure that the greatest percentage of entrained combustibles is oxidized.
Naegeli's combustor also negatively affects engine performance due to the increased back pressure resulting from exhaust flow restriction caused by the presence of the flame holder plate within the exhaust system piping. Additionally, given its substantial surface area, the flame holder plate is susceptible to fouling with oil or other components within the exhaust stream. Fouling may tend to plug penetrations in the flame holder plate which would further restrict the exhaust flow and negatively affect engine performance.
Accordingly, a need exists for a combustor system which can continuously and reliably enhance oxidation of uncombusted fuel, oil or other hydrocarbons entrained within the exhaust stream from an internal combustion engine to reduce overall pollutant levels and minimize discharge of uncombusted fuel and associated chemical components to the atmosphere, and particularly, to recreational or potable water supplies.